The present invention relates to communications methods and apparatus, and more particularly, to methods and apparatus for communicating facsimiles and data. Wireless communications systems are commonly employed to provide voice and data communications to subscribers. For example, analog cellular radiotelephone systems, such as those designated AMPS, ETACS, NMT-450, and NMT-900, have long been deployed successfully throughout the world. Digital cellular radiotelephone systems such as those conforming to the North American standard IS-54 and the European standard GSM have been in service since the early 1990""s. More recently, a wide variety of wireless digital services broadly labeled as PCS (Personal Communications Services) have been introduced, including advanced digital cellular systems conforming to standards such as IS-136 and IS-95, lower-power systems such as DECT (Digital Enhanced Cordless Telephone) and data communications services such as CDPD (Cellular Digital Packet Data). These and other systems are described in The Mobile Communications Handbook, edited by Gibson and published by CRC Press (1996).
FIG. 1 illustrates a typical terrestrial cellular radiotelephone communication system 20. The cellular radiotelephone system 20 may include one or more radiotelephones (mobile terminals) 22, communicating with a plurality of cells 24 served by base stations 26 and a mobile switching center or mobile telephone switching office (MTSO) 28. Although only three cells 24 are shown in FIG. 1, a typical cellular network may include hundreds of cells, may include more than one MTSO, and may serve thousands of radiotelephones.
The cells 24 generally serve as nodes in the communication system 20, from which links are established between radiotelephones 22 and the MTSO 28, by way of the base stations 26 serving the cells 24. Each cell 24 will have allocated to it one or more dedicated control channels and one or more traffic channels. A control channel is a dedicated channel used for transmitting cell identification and paging information. The traffic channels carry the voice and data information. Through the cellular network 20, a duplex radio communication link may be effected between two mobile terminals 22 or between a mobile terminal 22 and a landline telephone user 32 or another wireless communication network through a public switched telephone network (PSTN) 34. The function of a base station 26 is to handle radio communication between a cell 24 and mobile terminals 22. In this capacity, a base station 26 functions as a relay station for data and voice signals.
Recently, wireless communications systems have seen an increasing demand for services other than voice, including facsimile and data transmission associated with features such as internet access. Each of these services typically has different performance requirements. For example, facsimile systems are widely used to transmit images, typically of documents, from one location to another. Conventionally, a document is scanned by a xe2x80x9cfax machinexe2x80x9d to convert it into facsimile data which is then transmitted over a communications channel, typically a voice channel on the PSTN. The document is then reconstructed into hard copy from the transmitted facsimile data by a similar facsimile machine located at the other end of the communications channel.
Standard communications protocols have been developed for transmission of facsimile data. Older analog protocols, such as CCITT Group 1 and Group 2, are now generally obsolete. The digital CCITT Group 3 protocol, widely used by conventional office and home facsimile machines, uses digital modems transmitting digital facsimile data at speeds up to 9600 baud over conventional PSTN telephone lines. The Group 3 protocol includes handshaking and signal quality evaluation features which enable facsimile machines to step down the communication baud rate if the communications channel exhibits poor quality. A CCITT Group 4 protocol has also been established to provide less error-prone communication between facsimile machines over public data networks other than the PSTN.
Because of the increased mobility it offers, cellular radiotelephone technology is increasingly supplanting or being used in addition to the PSTN for many facsimile and data communications applications. Mobile cellular radiotelephones are now a common sight in businesses, home, and automotive environments. Personal computers have also been adapted for use with cellular radiotelephone communications systems, exchanging the wireline modem for a similar device acting over a cellular radiotelephone voice or data channel. In addition, wireless terminal devices have been introduced, referred to as Single Line Terminals (SLT), which provide an RJ-type interface typically associated with a PSTN to the user while utilizing a wireless communication link to the destination device for a call or, alternatively, to a PSTN which services the destination device.
One obstacle to implementation of facsimile communications over cellular radiotelephone communications systems is the generally lower bandwidth, lower signal quality, and higher communications costs which may be associated with cellular radiotelephone channels in comparison to conventional PSTN channels. One approach to providing more reliable radio transmission of facsimile data using packet data protocols with checking and retransmission features is described in U.S. Pat. No. 5,282,238 to Berland. An approach to sending faxes over analog cellular networks is described in U.S. Pat. No. 5,752,199 to Scott. Each of these approaches proposes ways to improve performance of facsimile transmission when a wireless channel is provided for this purpose.
The IS-136 communication standard, which provides for both analog and digital communication support, specifically supports Group 3 type facsimile transmissions. Under the IS-136 standard, a mobile terminal requesting communication access typically provides the communication network a service code. The service code may, for example, request analog speech, digital speech, analog or digital speech with a specified preference, asynchronous data or Group 3 type facsimile services from the IS-136 network. On receipt of a Group 3 facsimile service code, under the IS-136 standard, the communication system determines if a digital traffic channel is available.
Unfortunately, the PSTN in most locations does not support the transmission of a service code. Therefore, a problem is encountered with transmissions of data or facsimiles where the transmission path includes use of the PSTN to couple two wireless communication networks using service codes, such as two IS-136 systems. One proposed solution utilizes two stage dialing to provide a pilot number for transmission over the PSTN to communicate service code information. An example of two stage dialing is illustrated in FIG. 2.
As shown in the schematic illustration of FIG. 2, two stage dialing is provided for call setup because PSTN signaling typically does not support delivery of the service code which is, for example, on the IS-136 protocol, mandatory. Accordingly, the source device attempting to establish a channel to communicate data or a facsimile image 200 first transmits a pilot number to a wireless device such as the SLT 210. The pilot number carries service code information for the over air protocol, (such as IS-136,) as it is coherently related to the available service codes (i.e., a one to one unique correspondence is provided between pilot numbers and service codes supported by the over air protocol).
The single line terminal 210 receives the pilot number, determines the appropriate service code for the over air protocol and provides both the pilot number and the service code to the mobile switching center 28. The mobile switching center 28 provides a dial tone to the FAX/PC device 200 through the SLT 210. In other words, after receipt of the service code and pilot number from the SLT 210 over a control channel, such as a random access channel (RACH), the mobile switching center 28 allocates a traffic channel to the SLT 210 for use by the FAX/PC device 200.
On receipt of the dial tone, the FAX/PC device 200 transmits the destination number (also referred to as the B number (B#)) to the SLT 210 which in turn passes the destination number on to the mobile switching center 28 utilizing the assigned traffic channel.
Having received both the destination number and the pilot number, the mobile switching center 28 routes both the destination number (B#) and the pilot number through the PSTN 34 to the mobile switching center 28xe2x80x2 serving the remote wireless network associated with the destination number. The remote mobile switching center 28xe2x80x2 in turn passes the destination number and service code to the remote SLT 210xe2x80x2 associated with the destination number. Note that, once the service code associated with a facsimile transmission service is received by the mobile switching center 28, an additional protocol associated with the requested service, such as facsimile transmission, may be implemented and control subsequent transmissions. For example, in the case of a facsimile transmission as supported by the IS-136 over air protocol, once the associated service code is received, subsequent communications over the traffic channel will occur pursuant to the IS-135 protocol as well as the IS-136 over air protocol.
The additional user interaction required by two stage dialing is, however, generally undesirable for the user. Accordingly, there is a need for wireless communications systems and methods whereby multiple services with differing performance requirements can utilize a common infrastructure in an effective and efficient manner which is transparent to the user.
According to the present invention, methods, systems and mobile switching centers are provided that communicate a service code designation over a public switched telephone network without requiring two stage dialing. A received service code, for example, a request for facsimile transmission services, is converted by the mobile switching center receiving the request to a pilot number. Pilot numbers are coherently (uniquely) associated with each of the possible service codes supported by the communication protocol (such as IS-136) but are in a form which, unlike the service codes, may be transmitted over the PSTN. The conversion may be provided, for example, by a look up table maintained by the mobile switching center. On the destination end, the receiving wireless network mobile switching center may then convert the pilot number to a service code and establish a connection supporting the requested service to the destination device. Accordingly, the wireless device providing the service code may request services for a communication including establishment of a communication channel including the PSTN in the same manner as where the service is provided entirely by wireless networks which support communication of the service codes.
In one embodiment of the present invention, a method is provided for communicating a service code designation over a public switched telephone network (PSTN). A service code and a destination number are received from a wireless terminal on a control channel of a wireless communication network. The service code is converted to a pilot number which may be transmitted over the PSTN. In one embodiment, the service code is converted by looking up the pilot code in a cross reference memory that includes a unique pilot code associated with each of a plurality of service codes. The pilot number and the destination number are then communicated over the PSTN to a destination wireless communication network to provide the service code designation to the destination wireless communication network.
In another embodiment, the wireless communication network and the destination wireless communication network are IS-136 networks and the received service code requests at least one of facsimile or data services. In a further embodiment, the wireless terminal is a single line terminal (SLT) and the destination number is received by the SLT from either a facsimile device or a data device coupled to the SLT. In a further embodiment, the control channel over which the destination number and service code are received is a random access channel (RACH).
In a further embodiment of the present invention, the pilot number and the destination number are received over the PSTN at the destination wireless communication network. The service code is determined from the pilot number at the destination wireless communication network. A communication connection is then established supporting either facsimile or data services to a device associated with the destination number over the destination wireless communication network responsive to the determined service code.
In a further aspect of the present invention, a mobile switching center (MSC) is provided. The MSC includes a communication interface that communicates with a wireless device. A voice circuit coupled to the communication interface controls voice communication with the wireless device. An interworking circuit coupled to the communication interface controls at least one of data and facsimile communication with the wireless device. A PSTN interface couples the mobile switching center to a public switched telephone network (PSTN). In addition, the MSC includes a service code circuit coupled to the interworking circuit that converts a service code received from the wireless device to a pilot number which may be transmitted over the PSTN.
As will further be appreciated by those of skill in the art, while described above primarily with reference to method aspects, the present invention may also be embodied as systems.